The molded glass base for a screw type lamp, and in particular the base for larger flood lamps, is formed by coaxially positioning an eyelet, a threaded contact shell, and a lamp skirt in a mold. A gob of molten glass is then dropped in axially to cover the eyelet, and partially fill the volume of the shell. In a series of press moldings, the glass is forced to seal with the inner surfaces of the eyelet, and shell. The volume of glass pressed against the interior surface of the shell is forced to the edge of the shell where the glass flows around the end of the lamp skirt. During the series of moldings, a central lead channel is formed extending from the interior of the base through the eyelet. The eyelet lead channel subsequently receives, and has one of the lamp leads soldered or welded in place. In a similar fashion, a second lead channel is formed to pass through or around an end of the glass forming a side channel leading to the shell. A second lamp lead is passed through the second channel, and flattened against the exterior surface of the shell in a weld zone. The exposed end of the second lamp lead is then pressed hard against the weld zone of the shell and welded. The lamp may then be lit by providing power to the eyelet contact and the shell contact.
A problem may be encountered when the molded glass fails to seal with the shell opposite the weld zone. A gap then exists between the molded glass and the shell in the area of the second lead channel. When the second lead is welded to the shell, there is no solid glass wall bracing the weld zone of the shell, the shell flexes when the lead is pressed against the shell by the welding tool. The lead and shell are then not held as tightly against one another during welding as when the glass is properly sealed to the shell. The normally adequate weld pressure and heat are then inadequate when the second lead is welded, causing the weld to fail. The weld failure has occurred in from two to five percent of production, resulting in wasted material and energy. There is then a need to enhance the seal between the glass body and shell at least in the weld zone.
Examples of the prior art are shown in U.S. Pat. Nos. 3,796,528 and 3,840,954. Chrisman O. Smith U.S. Pat. No. 3,796,528 for Apparatus for Manufacturing an Electric Lamp Base that has a Snag-Proof Terminal issued Mar. 12, 1974 shows the lamp base structure and discusses the method of making molded lamp bases. Richard F. Hasell et al U.S. Pat. No. 3,840,954 for Method of Manufacturing and assembling an Electric Lamp Base shows a lamp base with a cemented in place lamp envelope.